Until now, surfaces that were to be electrolessly metallized were treated for catalytic metallization with either colloidal noble metal dispersions or with solutions of a stannous chloride-noble metal complex, or the areas that were to be metallized were first treated, for example, with a solution of stannous chloride and subsequently, after careful rinsing, with a solution containing a noble metal chloride. A substantial disadvantage of these known processes is the high cost due to the consumption of noble metal. Another disadvantage is that metal sensitization processes of this type require accurate supervision, not only in order to avoid loss of noble metal, but also in order to ensure that no noble metal films, which adversely affect the adhesion of the subsequently deposited metallic coatings, are formed on metallic areas.
Another method that has been proposed is to treat the surfaces that are to be sensitized first with a solution of a reducible metallic salt chosen from among copper, nickel, cobalt and iron salts and subsequently, preferably after drying, to reduce the deposited metallic salt by the action of heat or a reducing agent suitable for the particular metallic salt to form catalytically active metallic nuclei, and then to produce on the surface thus sensitized a metallic coating by electroless deposition by means of suitable baths. What has proved to be particularly disadvantageous is that surfaces catalytically sensitized in this manner show a relatively low catalytic activity and that for effective sensitization, i.e., formation of catalytically active nuclei, extremely active reducing agents are required, for which labor supervision and re-claiming are complicated and expensive.
The disadvantages described are avoided by use of the present invention, and the catalytic sensitization of plastic surfaces for electroless metallic deposition is achieved in a simple manner that is both operationally dependable and economical.
An object of the present invention is to make sensitizing solutions which are free from noble metals with high activity. A further object of the present invention is to sensitize surfaces for subsequent electroless metal deposition by means of a simple and economical process for the use and re-claiming of the sensitizing solutions.